Glutamate transport is essential for the synaptic inactivation of the neurotransmitter glutamate. A family of glutamate transporters has been identified in both astroglia and neurons. These transporters play important roles in the pathophysiology of neurologic disorders, notably amyotrophic lateral sclerosis and stroke. GLT1 is a glutamate transporter localized on astrocytes. We have determined that in a murine transgenic model of Huntington's Disease (HD) expressing Nterminally truncated huntingtin (N I 7182Q), there are decreased levels of GLT1, but not other glutamate transporter subtypes, in the striatum. In this proposal, experiments are presented to study the possible role of GLT1 and other molecular transporter subtypes in the development of striatal cell pathology seen in HD. First, a technique for the establishment of organotypic striatal cultures will be developed. These cultures will provide the ability to manipulate conditions, assess factors that affect GLT1 expression, and monitor for excitotoxic changes. Second, in order to further assess the role of GLT1 downregulation, behavior and striatal histology will be examined after GLT1 anti-sense infusion into rat striatum. Third, the regulation of glutamate transporters in N17182Q transgenic mice will be further evaluated in various brain regions and at various time points related to behavioral and histologic abnormalities. Human tissue from HD post-mortem brains will also be evaluated. The effect of upregulation of the GLT1 transporter subtype by the neurotrophin glialcell linederived neurotrophin (GDNF), and by the neuroinimunophilin GPI1046, will be evaluated in organotypic striatal cultures, and in vivo in transgenic HD mice. Finally, an EAAT2 (GLT1) overexpressing mouse will be crossed with transgenic mouse models of HD to determine if GLT1 over-expression can reverse some of the observed behavioral or pathologic phenotypes of HD.